1. Field of the Invention
This invention relates to a self-excited on-on type switching regulator.
2. Description of the Prior Art
Switching regulators can be generally classified into two types, i.e., self-excited type and separatelyexcited type. The separately-excited type has high freedom of design and is adaptable for all specifications, but is expensive, while the self-excited type has only limited freedom of design but is suitable when it is desired to reduce cost. The self-excited type of power transformation usually employs the flyback type and rarely uses the on-on type. This is because with the on type, difficulty is encountered in an attempt to balance a current which is caused to flow from a choke coil of a rectifying-smoothing circuit to a load when an oscillation transistor is in an "off" state, and excitation energy which is accumulated in the choke coil when the oscillation transistor is in an "on" state. More specifically, in a self-excited oscillator circuit such as blocking oscillator circuit or the like, an oscillation transistor will be turned on when magnetic flux in an oscillation transformer becomes extinct, but with a certain load, it may happen that excitation is effected while magnetic flux still remains in the choke coil. If such a condition occurs repeatedly, the choke coil will be saturated with magnetic flux, so that when the oscillation transistor is turned on, an excessive surge current resulting from excitation energy of the choke coil will be caused to flow through the transistor. For this reason, it is difficult to protect the transistor from being damaged by the excessive surge current. However, the flyback type requires a larger transformer since a current which is caused to flow through the secondary winding of a transformer is about twice as high as that in the on-on type. The on-on type is preferred.